part 3] MINERALS IN CORAL-LIMESTONE 8 OF BARBADOS. 107 



both as separated from the corals of the limestones and from the 

 beach-rocks by very dilute acid, and after treatment with hot 

 sulphuric acid followed by a weak alkaline solution, prove that in 

 every case the extraneous mineral constituents consist of hydrated 

 aluminium silicate — kaolin or halloysite — usually deeply stained 

 with limonite, Hakes of orange-yellow limonite, minute fragments 

 of red haematite, and many specks of minerals, felspars, and pyro- 

 xene, with flakes of both acidic and basic volcanic glass which not 

 infrequently are enclosed and hidden in minute masses of kaolin, 

 haematite, or limonite. 



The fragments of minerals and splinters of glass contained 

 in the corals are fresh and quite unaltered in appearance; they are 

 characterized by sharply-angular outlines, and, in the case of the 

 glass-splinters, by conchoidal fracture. Hence I regard them as 

 being wind-borne volcanic debris which have been largely protected 

 from weathering agencies by their enclosure in the limestone. 

 Those in the clastic limestone or beach-rock show evidence of 

 detrition and weathering prior to the consolidation of the limestone.. 



The direct microscopical examination of the residua separated 

 from the corals and beach-rocks by very dilute acid showed that, 

 if the examinations were not specially directed towards the search 

 for mineral fragments, the extraneous mineral constituents would 

 be regarded as consisting essentially of kaolin and limonite with 

 only negligible specks of felspar and possibly of quartz. 



These observations and analyses indicate that the extraneous 

 mineral matters in the high-level limestones were derived from 

 volcanic sources, while their limonite, kaolin, or halloysite, and 

 secondary crystalline or chalcedonic silica, where it occurs, are the 

 normal decomposition or weathering products of lime-soda felspars 

 and of ferromagnesian minerals, both of which classes of minerals 

 are present in relatively high proportions in the unaltered recent 

 volcanic ash from the Soufriere of St. Vincent and from Moni 

 Pele, Martinique. The lime-soda felspars and ferromagnesian 

 minerals are of comparatively rare occurrence in the residua of the 

 high-level beach-rock, and hence much of them which may have 

 originally been present in the volcanic ash has been altered into 

 Limonite, kaolin, and secondary silica by detrital and weathering 

 actions. 



The extraneous minerals in the low-level limestones are more 

 varied than are those in the high-level limestones, and contain 

 lime-soda felspar and pyroxene in considerable proportions ; they 

 also contain quartz in fair quantities, derived probably from the 

 older Scotland Beds, which at the time of their formation were 

 higher in altitude than the low-level Limestones and hence were ex- 

 posed to atmospheric detrition and degradation, their constituents 

 being washed, as at present, into the surrounding sea during heavy 

 rainfalls. 



If my deduction as to the origin of the extraneous mineral 

 constituents of the high-level limestones is correct, evidence of 

 the present or former existence of volcanic minerals should be 



